The key to controlling a DC brushless motor lies in that a rotor position is detected, then a phase change point is obtained according to a position information, a corresponding stator winding is energized for phase change, and an energizing current is synchronous with a counter electromotive force phase of the winding. An electric tool needs to be started with a full torque on a majority of application occasions. The full-torque start may be achieved upon control with a sensor, but a mounting error exists and substantially affects direction change and reduces an efficiency of the whole machine particularly when a motor with a larger number of pole-pairs is running at a high speed.